1. Field of the Invention
This invention relates to a system for controlling a gas discharge display device for shifting discharge spots and more precisely, to a system for controlling the direction of the shifting.
2. Description of the Prior Art
The dot matrix type display device, called a plasma display panel, is one of the known display devices utilizing gas discharge. The conventional plasma display panel is described in various publications, for example, U.S. Pat. No. 3,499,167 entitled "Gas discharge display memory device and method of operating" by Baker et al., and U.S. Pat. No. 3,559,190 entitled "Gaseous display and memory apparatus" by Bitzer et al. Such a plasma display panel comprises a discharge space filled with gas capable of ionization and arrays of X and Y electrodes arranged and connected in matrix form so as to provide many elemental discharge cells or discharge points in the display panel. A major characteristic feature is a memory function due to the wall charge which accumulate at the discharge points on insulating layers covering the electrodes. However, the circuit for driving this plasma display panel requires one address circuit for each X and Y electrode. As these address circuits are required to scan sequentially, the peripheral circuit of this plasma display panel becomes very complex and expensive. In this connection, the conventional plasma display panel is disadvantageous compared with other devices such as cathode ray tube display devices.
Another display device utilizing gas discharge employs self scanning as a means for resolving the above-mentioned inconveniences of the peripheral circuit, known as a "Self Scan (Trademark) device". This kind of display device, as described, for example, in ELECTRONICS (in u.s.a.) Vol. 43, No. 5, P120-P125, comprises double construction of the scanning part and the display part. Discharge spots are moved along each line of the scanning part on the rear face, which is used as an exciting source. The discharge spots are scanned and selectively taken to the display part on the front face, in accordance with the position of said discharge spot, and thereby the display action is carried out.
However, the above-mentioned type of display device utilizing gas discharge has various disadvantages. The construction of a wall, for separating the scanning part and the display part, and the construction of the electrodes is complicated and is not suited to mass production. Also the life of each electrode exposed directly to the discharge space is short, and an external memory for refreshing the display spots is necessary. Further the brightness of the display part decreases as the number of picture elements increases.
Still another display device, which is called the "Self shift type plasma display panel," is disclosed in U.S. Pat. No. 3,944,875 entitled "Gas discharge device having a function of shifing discharge spots" by Owaki et al.
Such a self shift type plasma display panel comprises a discharge space filled with gas capable of ionization, at least one row electrode and a plurality of column electrodes positioned in the direction transverse to the row electrodes.
However, the shifting of discharge spots is conventionally provided for in only one direction, so that when it is necessary to correct written information the content of the entire line containing the errors must be rewritten. Accordingly, when miswritten parts are discovered in the written information, the portion which is incorrectly written should be rewritten. Further, since the conventional self-shift always occurs in one direction, when it is necessary to display a few characters at the end opposite from the WRITE electrodes the written characters must be shifted there from the WRITE electrodes. Also, the information which is written to the device is frequently required to be transferred to and READ by a separate information processing device.